Repairing a Flooded Lawn

Tom Kalb, Extension Horticulturist

After flooding devastates a lawn,  the first step is to pick up any garbage and other debris the floodwaters brought into the yard. Be careful as pieces of glass, metal and other harmful items may be buried in the silt. Wash up thoroughly after working with the soil since it may have been contaminated with toxic materials.

Lawns under water for less than four days and covered with one inch or less of silt may quickly recover. In this case, gently rake the ground to break the soil crust. Core aeration can help dry the soil. A half-strength fertilizer application (1/2 pound of actual nitrogen per 1,000 square feet) will encourage turf recovery. Fall overseeding may thicken the lawn.

Lawns under water for more than four days and/or covered with more than one inch of silt will require major renovation. Much, if not all, of the turf is dead.

Start by grading the landscape, trying to get it back to its original topography as much as possible. Accumulations of silt greater than three inches should be scraped away. Severely eroded areas should be replenished with topsoil. As a general rule, at least four inches of topsoil is needed for a healthy lawn.

Cultivate the area, incorporating the silt into the topsoil. Prepare a smooth seedbed and apply a starter fertilizer.

Seeding is best done from mid-August to mid-September in North Dakota. Spring is the second best time of the year to sow. Use hardy grass types normally used in the region, such as Kentucky bluegrass, red and other fine fescues, perennial ryegrass, crested wheatgrass and blue grama grass. Flood-tolerant grasses, such as reed canary grass, are too coarse and not recommended for home landscapes.

New sod can be applied through mid-October. Sod typically is a Kentucky bluegrass mix and should be used only in sunny areas.

For more information, see NDSU publication H1311 "Home Lawn Establishment" at www.ag.ndsu.edu/pubs/plantsci/landscap/h1311.pdf.